In order to handle increasing communication traffic in recent years, a further increase in communication capacity is desired. In optical communication systems using conventional single mode optical fibers, however, a limit to increasing capacity is predicted. As a technique to overcome the limit, active research and development of space division multiplexing have been carried out. Optical fibers to implement space division multiplexing include multicore fibers (MCFs) which have a plurality of cores and where a transmission capacity is increased by transmitting information to each of the cores.
The MCFs are roughly classified into two types of uncoupled MCFs where each core individually transmits information and coupled multicore fibers (C-MCFs) where respective cores are coupled and thereby form supermodes and information is transmitted by each supermode. In order to perform high-quality transmission in uncoupled MCFs, it is important to reduce crosstalk (XT) between each of the cores as well as it is necessary to measure and evaluate the XT.
The following conventional arts 1 to 4 are listed as the conventional techniques of measuring XT.
1. A method of measuring transmission power of light incident on a certain core using a power meter (Non-Patent Document 1)
2. A method using a multi-channel OTDR (Patent Document 1)
3. A method using a bi-directional OTDR (Patent Document 2)
4. A method using a power change amount due to multipath interference of each core for an XT evaluation (Non-Patent Document 2)
Non-Patent Documents 3 to 5 are described below.